1. Field of the Invention
The present invention relates to an image signal processing apparatus for reading an original image through an image signal input device such as a scanner or the like to thereby obtain image information, and particularly relates to an image signal processing apparatus for correcting the displacement of image information at the time of reading the image information irrespective of the outline of a rectangular image.
2. Description of the Prior Art
Most of image signals fetched by an image signal input device such as a scanner or the like have inclination or displacement caused by user's manipulation or mechanical structure. Some methods have been proposed for correcting such displacement or the like.
For example, Japanese Patent Unexamined Publication No. Sho. 61-187082 discloses a method for correcting inclination of image information by assigning a central point of rotation and an aim point of rotation to a rectangular image obtained through reading an original document.
FIG. 8 shows a procedure of correction in the conventional example disclosed in the above publication, in which the reference numeral 801 designates an image signal display means, 802 designates an inclined input image, that is, an input image to be corrected, displayed on the image signal display means 801, and 803 designates a predetermined area in which the input image 802 is to be positioned after it is corrected.
In the conventional example disclosed in the above publication, an image signal fetched through an image signal input device is developed on an image memory while the image signal is inclined. In order to correct the inclination, first, a user uses a light pen or a cursor to indicate an origin 804 of rotation and a designated point 805 of the input image 802 for coinciding the input image 802 with the predetermined area 803. Thereafter a rotation section computes the angle between a straight line 806 connecting the origin 804 and the designated point 805 and a left end line of the predetermined area 803, computes vertical and horizontal quantities of movement required for coinciding the input image 802 with the predetermined area 803, and shifts image data in the vertical and horizontal directions on the image memory on the basis of the computation to thereby correct the inclination of the image.
In the conventional example disclosed in the above publication, in order to perform rotation processing, it is necessary for a user to confirm through his eyes the positions of angles and the inclination of sides of the input image 802 having a rectangular shape to indicate the origin 804 and the designated point 805. If the input image is not rectangular, therefore, it is very difficult, or impossible in some cases, to indicate the origin 804 and the designated point 805.
Further, such correction can be applied to only the whole of an input image, and cannot be applied to any cut piece of the image. That is, indeed, the inclination of an input image can be judged from the inclination of the frame of the input image if the whole of its original image is inputted, but if a portion of the input image is displayed, it is impossible to judge the inclination of the input image from the frame of this partial input image.
Further, there has been a problem that it is impossible to apply such correction to the case of a large quantity of correction. That is, if the quantity of correction (displacement or inclination from an original document) is so large to exceed beyond a read area of a scanner or the like, for example, if it is impossible to indicate the origin 804, the method disclosed in the above publication cannot be applied to such a case.